Acoustic touch apparatus with multi-touch capability

ABSTRACT

An acoustic touch apparatus that utilizes the transfer of surface acoustic waves from one surface, through the touch substrate, to another surface to enable multi-touch capabilities.

FIELD OF THE INVENTION

This invention generally relates to touch sensor systems and, moreparticularly to, surface acoustic wave (SAW) touchscreens withmulti-touch capability.

BACKGROUND OF THE INVENTION

Touch sensor systems, such as touchscreens or touch monitors, can act asinput devices for interactive computer systems used for variousapplications, for example, information kiosks, order entry systems,video displays, etc. Such systems may be integrated into a computingdevice, thus providing interactive touch capable computing devices,including computers, electronic book readers, mobile communicationsdevices, trackpads, and touch sensitive surfaces more generally.

Generally, touch sensor systems enable the determination of a positionon the surface of a substrate via a user's touch of the surface. Thetouch substrate is typically made of some form of glass which overlies acomputer or computing device display, like a liquid crystal display(LCD), a plasma display, etc. The touch sensor system is operativelyconnected to the device display so that it also enables thedetermination of a position on the device display and, moreover, of theappropriate control action of a user interface shown on the display.Alternatively, the touch substrate may be opaque such as for trackpadapplications where the display may be located away from the touchsensor.

Touch sensor systems may be implemented using different technologies.Acoustic touch sensors, such as ultrasonic touch sensors using surfaceacoustic waves, are currently one of the major touch sensor technologiesand many types of acoustic touch sensors now exist. For example, a“non-Adler-type” acoustic touch sensor uses a number of transducers percoordinate axis of the sensor substrate to spatially spread atransmitted surface acoustic wave signal and determine the touch surfacecoordinates by analyzing spatial aspects of the wave perturbation from atouch of the touch surface. An “Adler-type” acoustic touch sensor usesonly two transducers per coordinate axis to spatially spread atransmitted surface acoustic wave signal and determine the touch surfacecoordinates by analyzing temporal aspects of a wave perturbation from atouch. For each axis of the substrate of the “Adler-type” sensor, onetransducer at a respective peripheral surface generates surface acousticwave pulses that propagate through the substrate across a perpendicularperipheral surface along which a first reflective grating or array isdisposed. The first reflective array is adapted to reflect portions of asurface acoustic wave perpendicularly across the substrate along pluralparallel paths to a second reflective array disposed on the oppositeperipheral surface. The second reflective array is adapted to reflectthe surface acoustic wave along the peripheral surface to a secondtransducer at a respective perpendicular peripheral surface where thewave is received for processing. The reflective arrays associated withthe X axis are perpendicular to the reflective arrays associated withthe Y axis so as to provide a grid pattern to enable two-dimensionalcoordinates of a touch on the substrate to be determined. Touching thesubstrate surface at a point causes a loss of energy by the surfaceacoustic waves passing through the point of touch. This is manifested asan attenuation of the surface acoustic waves. Detection circuitryassociated with each receiving transducer detects the attenuation as aperturbation in the surface acoustic wave signal and performs a timedelay analysis of the data to determine the surface coordinates of atouch on the substrate. This type of sensor is shown in FIG. 1 anddescribed in more detail below.

Historically, the operative elements of an acoustic touch sensor, i.e.,the transducers and reflective arrays, which are on the front surface ofthe substrate, have been covered and hidden from view by a protectivebezel provided by the housing of the touch sensor or the deviceintegrating the sensor. Current trends eliminate the bezel in favor offlush surroundings of touch area, even for larger-sized devices.Moreover, possible future applications of touch technology, such asturning passive objects like glass table tops into touch input devicesand endowing robots with a sense of touch in their exterior shells,further motivate moving the operative elements from the exterior touchsensing surface of the touch substrate to the protected and hiddeninterior surfaces of the substrate. Acoustic touch sensors may utilize arounded-substrate-edge approach to obtain such a zero-bezel orbezel-less design. This type of sensor is also described in more detailbelow.

Recently, acoustic touch sensors having multi-touch capability have beenintroduced into the commercial marketplace. Multi-touch capability isgenerally defined as the ability of a touch sensor to sense or recognizetwo or more (i.e., multiple) simultaneous touch points. Multiplesimultaneous touch points include, for example, pinching gestures,parallel line swipes, and pivoting movements. To date, acoustic touchsensors, such as the IntelliTouch™ Plus touch sensors by TycoElectronics Corporation have been able to deliver dual touchperformance. Certain other touch technologies are even providing higherlevels of multi-touch performance. The competition between the differenttechnologies and the increase of system applications using multi-touchis now increasing the expectation and demand by users and designers forgood touch performance not only for dual touches but also for three ormore simultaneous touches.

A difficulty for acoustic touch sensors to support two or moresimultaneous touches rests on such sensors not being able to acquiresufficient, clear coordinate information to match respective Xcoordinates with the respective corresponding Y coordinates of themultiple touches. The difficulties increase as the number ofsimultaneous touches increases.

SUMMARY OF THE INVENTION

The present invention obviates the above problems by providing anacoustic touch apparatus that distinguishes simultaneous touches,comprising a substrate that is adapted to utilize a transfer of surfaceacoustic waves, through the substrate, between opposite surfaces of thesubstrate to vary touch sensitivity along a respective acoustic pathacross a substrate touch region and acoustic transducers that areadapted to transmit and receive surface acoustic waves travelling on theopposite substrate surfaces, said substrate touch region providingadditional signal information of touch responses of receivingtransducers sufficient to permit the apparatus to determine an axiscoordinate of a respective touch on the substrate touch region. Theadditional signal information may comprise a comparison of the touchresponses of receiving transducers with non-touch responses of thereceiving transducers. Alternatively, the additional signal informationmay comprise a comparison of the touch responses of receivingtransducers with non-touch responses of the receiving transducers.

The present invention also provides an acoustic touch apparatus,comprising: a substrate that has top and bottom surfaces; a transmittingand receiving acoustic wave transducer pair on the top surface that isadapted to transmit and receive surface acoustic waves therebetweenacross a touch region on the top surface and to produce a touch responsesignal for a touch on the touch region; a transmitting and receivingacoustic wave transducer pair on the bottom surface that is adapted totransmit and receive surface acoustic waves therebetween, said substratebeing adapted to propagate surface acoustic waves along each surface andto transfer, through the substrate, surface acoustic waves between thesurfaces sufficient to enable a touch on the top surface to produce atouch response signal by the bottom surface transducer pair; and acontroller that operates on the touch response signals and non-touchresponse signals produced by each of the bottom surface transducer pairand the top surface transducer pair and determines positionalinformation of a touch on the touch region from the response signals.

The controller may operate on the response signals to determine the topand bottom touch sensitivity along an acoustic path across the touchregion. The top and bottom sensitivity may be represented by thereduction in amplitude of the touch response signal to the non-touchresponse signal for each of the bottom surface transducer pair and thetop surface transducer pair. Further, the controller may determinepositional information of a touch by comparing the amplitude reductionsof the touch response of the bottom surface transducer pair to the touchresponse of the top surface transducer pair. Alternatively, thecontroller may determine positional information of a touch by applyingthe following relation: b(d)/t(d)={b(L/2)/t(L/2)}·d·(L−d)/(L/2)², whereL is the distance between the transducers in a respective transducerpair on the top and bottom surfaces; b(d) is the amplitude reduction ofthe touch response for a touch at distance d by the bottom surfacetransducer pair; and t(d) is the amplitude reduction of the touchresponse for a touch at distance d by the top surface transducer pair.

The substrate may be adapted to propagate surface acoustic waves alongeach surface and to transfer, through the substrate, surface acousticwaves between the surfaces sufficient to enable a touch on the topsurface to produce a respective touch response signal between the topsurface transmitting transducer to the bottom surface receivingtransducer, and the bottom surface transmitting transducer to the topsurface receiving transducer. In such case, the top and bottomsensitivity may be represented by the reduction in amplitude of thetouch response signal to the non-touch response signal between thebottom surface transmitting transducer to the top surface receivingtransducer, and the top surface transmitting transducer to the bottomsurface receiving transducer. Further, the controller may determinepositional information of a touch by comparing the amplitude reductionsof the touch response of the bottom surface transmitting transducer tothe top surface receiving transducer, to the touch response of the topsurface transmitting transducer to the bottom surface receivingtransducer. Further, the controller may determine positional informationof a touch by further analyzing the amplitude changes of the touchresponse of the bottom surface transducer pair and of the touch responseof the top surface transducer pair. The controller may also determinepositional information of overlapping touches on the top surface byutilizing a comparison of the touch response signal between the topsurface transmitting transducer to the bottom surface receivingtransducer with the touch response signal between the bottom surfacetransmitting transducer to the top surface receiving transducer for eachtouch to distinguish between the signals of the touches and therespective positional information.

The present invention also provides an acoustic touch sensor systemhaving multi-touch capability, comprising: a substrate that is capablein a peripheral region to propagating surface acoustic waves alongsubstrate surfaces and in a central region to permit top-bottomoscillation of the surface acoustic waves from the one of the surfacesto the other surface through the substrate, said substrate having a topsurface, a bottom surface, and a curved connecting surface formedbetween said top surface and said bottom surface; a first transmittingelement disposed on an outside area of the peripheral region of thebottom surface and a second transmitting element disposed on an insidearea of the peripheral region of the bottom surface; a first receivingelement disposed on an outside area of the peripheral region of thebottom surface and a second receiving element disposed on an inside areaof the peripheral region of the bottom surface, the set of transmittingelements and the set of receiving elements disposed on opposing sides ofthe central region of the substrate; and a controller that excites thefirst and second transmitting elements to generate respective surfaceacoustic waves and that analyzes the respective signals received by thefirst and second receiving elements, said substrate forming at leastrespective wave paths from the first transmitting element, around theproximate curved connecting surface, through the substrate in thecentral region and to the second receiving element; and from the secondtransmitting element, through the substrate in the central region,around the proximate curved connecting surface and to the firstreceiving element.

Each transmitting element may comprise a transmitting acoustic wavetransducer and an associated transmitting reflective array and eachreceiving element may comprise a receiving acoustic wave transducer andan associated receiving reflective array. Also, the system may furthercomprise another set of transmitting elements and another set ofreceiving elements disposed on the other two opposing sides of thecentral region of the substrate in a similar manner as the respectivefirst sets, each pair of sets being utilized to define a respective axiscoordinate of the front surface. Also, the substrate may further have adamping material separating the peripheral region into outside andinside areas. Also, the substrate may be adapted to providenon-symmetrical top and bottom surfaces acoustic waves in a peripheralregion in order to propagate surface acoustic waves.

Also, each receiving element may be adapted to produce a touch responsesignal for a respective touch on the top surface and the controlleranalyzes the touch response signals and non-touch response signalsproduced by each receiving element to determine axis coordinateinformation of the touch on the top surface from the response signals.In such case, the controller may analyze the ratios of signal losses, orthe ratios of signal level changes, of touch response signals todetermine axis coordinate information of the touch on the top surface.Alternatively, the controller may analyze the delay times of touchresponse signals, and the ratios of signal losses of touch responsesignals in the top-bottom oscillation-based signals to determine axiscoordinate information of the touch on the top surface. In such case,certain of the axis coordinate information may be dependent upon theratios of signal losses of touch response signals in the top-bottomoscillation-based signals; and the distance between respectivetransmitting and receiving elements on the top and bottom surfaces.Another set of transmitting elements and another set of receivingelements may be disposed on the other two opposing sides of the centralregion of the substrate in a similar manner as the respective firstsets, each pair of sets being utilized to define a respective axiscoordinate of the front surface.

Advantageously, the present invention provides an acoustic touch sensorwith sets of two to four signals providing the same time delayinformation on a coordinate perpendicular to the acoustic path throughthe touch area and for which ratios of the touch sensitivity provide atleast a rough measurement of a coordinate parallel to the acoustic paththrough the touch area. Thus, for example, a set of X signals not onlyprovides a precise X coordinate but also a rough Y coordinate thusremoving the usual X-Y association ambiguity problem. Furthermore, theset of X signals can be used to separate overlapping shadows of pairs oftouches with similar X coordinates via identifying minimum width linearcombinations of shadows in different members of the set of X signals.The present invention treats sets of Y signals similarly.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is madeto the following description of exemplary embodiments thereof, and tothe accompanying drawings, wherein:

FIG. 1 is a front plan view of a substrate of a typical surface acousticwave touch sensor;

FIG. 2 is an illustration of top-bottom oscillation phenomenon in a thinsubstrate;

FIG. 3 a is a side perspective of an acoustic touch sensor constructedin accordance with the present invention;

FIG. 3 b is a simplified transparent view of the substrate of the sensorof FIG. 3 a;

FIG. 3 c is a schematic view of a touch surface of a substrate of atypical acoustic touch sensor with sample multiple touch pointsindicated;

FIG. 3 d is a simplified side view of the substrate of the sensor ofFIG. 3 a with a corresponding chart of a touch response;

FIG. 3 e is a simplified side view of another substrate of the sensor ofFIG. 3 a with a corresponding chart of a touch response;

FIG. 3 f is an additional corresponding chart of a touch response forthe substrate of FIG. 3 e;

FIG. 4 a is a side perspective of a second acoustic touch sensorconstructed in accordance with the present invention;

FIG. 4 b is a back plan view of the substrate of the sensor of FIG. 4 a;

FIG. 4 c is a simplified side view of the substrate of FIG. 4 b;

FIG. 5 is a graph of touch sensitivity for the substrate of FIG. 4 b;

FIG. 6 a is a schematic view of a touch surface of a substrate of anacoustic touch sensor of the present invention with sample multipletouch points indicated; and

FIGS. 6 b-6 d are graphs of the signals processed by the sensor of FIG.6 a during a multi-touch operation.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

FIG. 1 shows a front plan view of a substrate 12 of a typical“Adler-type” surface acoustic wave touch sensor 10. As noted above, thetouch sensor 10 uses two transducers per coordinate axis to spatiallyspread a transmitted surface acoustic wave signal and determine thetouch surface coordinates by analyzing temporal aspects of a waveperturbation from a touch. Accordingly, for the X coordinate axis, afirst transmitting transducer 14 a at a respective peripheral surfacegenerates surface acoustic wave pulses that propagate through thesubstrate 12 across a perpendicular peripheral surface along which afirst reflective grating or array 16 a is disposed. The first reflectivearray 16 a is adapted to reflect portions of a surface acoustic waveperpendicularly across the substrate 12 (across the so-called “the touchsurface” 18) along plural parallel paths to a second reflective array 16b disposed on the opposite peripheral surface. The second reflectivearray 16 b is adapted to reflect the surface acoustic wave along theperipheral surface to a first receiving transducer 14 b at a respectiveperpendicular peripheral surface where the wave is received forprocessing. Similarly, for the Y coordinate axis, a second transmittingtransducer 14 c at a respective peripheral surface generates surfaceacoustic wave pulses that propagate through the substrate 12 across aperpendicular peripheral surface along which a third reflective gratingor array 16 c is disposed. The third reflective array 16 c is adapted toreflect portions of a surface acoustic wave perpendicularly across thesubstrate 12 (i.e., the touch surface 18) along plural parallel paths toa fourth reflective array 16 d disposed on the opposite peripheralsurface. The fourth reflective array 16 d is adapted to reflect thesurface acoustic wave along the peripheral surface to a second receivingtransducer 14 d at a respective perpendicular peripheral surface wherethe wave is received for processing. The reflective arrays 16 a, 16 bassociated with the X coordinate axis are perpendicular to thereflective arrays 16 c, 16 d associated with the Y coordinate axis so asto provide a grid pattern to enable two-dimensional coordinates of atouch on the substrate 12, and more specifically, the touch surface 18,to be determined.

Touching the touch surface 18 at a point causes a loss of energy by thesurface acoustic waves passing through the point of touch. This ismanifested as an attenuation of the surface acoustic waves. Detectioncircuitry associated with each receiving transducer 14 b, 14 d detectsthe attenuation as a perturbation in the surface acoustic wave signaland performs a time delay analysis of the data to determine the surfacecoordinates of a touch on the touch surface 18.

Varying the touch sensitivity along the acoustic path across the touchregion of the substrate may be beneficial in acquiring additionalcoordinate information. In this way, the touch sensor may be able todistinguish between real touch points and “ghost touch points” (i.e., Xand Y coordinate pairs corresponding to a location with no physicaltouch but rather an X coordinate from one true touch mismatched with a Ycoordinate of a different true touch) in processing the touch signals.This would enable the detection circuitry to match a respective Xcoordinate with a respective corresponding Y coordinate for each touchpoint of multiple simultaneous touches.

One method of modulating the touch sensitivity along the acoustic pathalong the touch region would be to utilize a unique property of surfaceacoustic waves generated for an acoustic touch sensor. Specifically,surface acoustic waves propagating on one surface of a substrate maytransfer, under certain circumstances, through the substrate to theother surface. Generally, this transfer can occur when the depth of thesubstrate is sufficiently small. The current standard used in acoustictouch sensors is approximately 3 mm, thick substrate. It has beenpreviously reported that the typical substrate (i.e., soda-lime glass)of an acoustic touch sensor, using the standard transmitting frequencyof 5.53 MHz, should be at least 2 mm thick for propagating surfaceacoustic waves, that is, at least 3.5 Rayleigh wavelengths thick. Thesepropagating surface acoustic waves are maintained on the substratesurface of the transmitting transducer, much as surface waves on theocean are maintained on the ocean surface, although in both cases wavemotion and power penetrates some depth into the wave medium of glass orwater. However, at certain smaller thicknesses, the surface acousticwave energy becomes transferred (actually oscillates) between the twoopposing surfaces of the substrate. This is further described incommonly-owned U.S. patent application Ser. No. ______ entitled,“Acoustic Touch Apparatus With Variable Thickness Substrate”, (Attorneydocket ET-01124-US) concurrently filed in the name of David Hecht andJoel Kent, which is hereby incorporated by reference.

Briefly, the transmitting transducers of an acoustic touch sensornormally produce a surface acoustic wave which is typically termed aRayleigh wave. A Rayleigh wave has vertical and transverse wavecomponents with substrate particles moving along an elliptical path in avertical plane including the axis of wave propagation, and wave energydecreasing with increasing depth in the substrate. Mathematically,Rayleigh waves exist only in semi-infinite media. In plates orsubstrates of finite thickness, such as those used in acoustic touchsensors, the waves are more precisely termed quasi-Rayleigh waves, eachof which comprises a superposition of equal portions of the lowest ordersymmetric and anti-symmetric Lamb wave modes S₀ and A₀. For substratesof thickness of interest for acoustic touch sensors, the S₀ Lamb wavemode is essentially a surface acoustic wave on the transmittingtransducer (or top) surface simultaneous with an in-phase surfaceacoustic wave on the opposing (or bottom) surface, while the A₀ Lambwave mode is similar except the surface acoustic wave on the bottomsurface is out of phase with the surface acoustic wave on the topsurface. A quasi-Rayleigh wave on the top surface is a positivesuperposition of the two wave modes (i.e., S₀+A₀) which cancels thesurface acoustic wave on the bottom surface and a quasi-Rayleigh wave onthe bottom surface is a negative superposition of the two wave modes(i.e., S₀−A₀) which cancels the surface acoustic wave on the topsurface. A transmitted (or launched) pure S₀ or A₀ wave will foreverremain a S₀ or A₀ wave, respectively, since each is a true mode ofvibration. In contrast, neglecting glass attenuation, a launched topquasi-Rayleigh wave, which is not a true mode of vibration, willeventually convert into a bottom quasi-Rayleigh wave and the two waveswill continue to oscillate back and forth in a beat pattern. This isbecause the wave modes S₀ and A₀ have slightly different phasevelocities so that the A₀ phase relative to the S₀ phase continuallychanges and with enough distance S₀+A₀ becomes S₀−A₀ and then backagain, repeatedly in a beat pattern. This is an example of the classicalcoupled oscillator system that occurs in many contexts. The result issurface wave energy is transferred back and forth between the top andbottom surfaces of the substrate, as indicated above.

FIG. 2 is an illustration of this top-bottom oscillation for a thinsubstrate 20 that may be used in an acoustic touch sensor. Neglectingattenuation effects, if “x” is the distance of propagation away from awedge transducer 22 continuously excited at frequency f, the waveamplitude (e.g. vertical particle displacement) on the top surfaceT(x,t) and the wave amplitude on the bottom surface B(x,t) will varywith position and time as follows, where k is the Rayleigh wavelength atfrequency f and A is a beat wavelength that characterizes theoscillation of the Rayleigh wave between surfaces:

T(x,t)=Constant·cos(πx/Λ)·cos(2πx/λ−2πf·t) and

B(x,t)=Constant·sin(πx/Λ)·sin(2πx/λ−2πf·t).

It is important to note that, in half a beat wavelength, Λ/2, a Rayleighwave on one surface is completely transferred to the other surface. Thetime averaged power transfer between Rayleigh waves on the two surfacesis schematically represented by the solid line arrows and isproportional to sin(2πx/Λ), where a positive algebraic sign signifiespower transfer from top to bottom and a negative sign signifies powertransfer in the other direction. Where either the top or bottomamplitude is small, the power transfer is also small.

The phenomenon of top-bottom oscillation is conventionally regarded as aproblem to avoid in acoustic touch sensor design so as to maintainpropagating surface acoustic waves on a respective surface. And for thispurpose, the touch substrate is designed as a rule to be at least 3 or 4Rayleigh wavelengths thick to essentially eliminate top-bottomoscillations (although there may be other ways like the use of substratecoatings to suppress the oscillations). A substrate of 3.5 Rayleighwavelengths is generally sufficient to suppress top-bottom oscillationsand a substrate thickness of 5.5 Rayleigh wavelengths is sufficient toconfidently eliminate top-bottom oscillations for all plausibleengineering situations.

The key engineering parameters to consider are the transmittingfrequency, the distance across the substrate (i.e., the top-bottomoscillation distance) required for a top surface acoustic wave toconvert into a bottom surface acoustic wave (and vice versa), thethickness of the substrate, and the acoustic path lengths of the touchsensor. The composition of the substrate is also a factor. Generally,though, the thinner the substrate, the shorter the distance for thistop-to-bottom energy transfer. If the top-bottom oscillation distance isthen comparable or short compared to the acoustic path lengths, then thesurface wave energy will not be maintained on the top surface.Consequently, the surface acoustic wave launched on one surface of thesubstrate will appear on the other surface.

The surface acoustic wave energy that is propagating across the touchregion surface transfers between the top and bottom surfaces thuschanging the fraction of surface acoustic wave energy at the touchregion surface. This results in a modulation of touch sensitivity alongthe acoustic path across the touch region surface. It would beadvantageous to utilize this process to acquire additional and clearcoordinate information of multiple simultaneous touches for acoustictouch sensors.

FIG. 3 a shows a simplified side perspective of an acoustic touch sensor50 constructed in accordance with the present invention. The touchsensor 50 is similar in construction to the sensor 10 of FIG. 1 with theaddition of an identical transducer-array arrangement on the oppositeside of the substrate 51. As described in further detail below, thisconfiguration in combination with the top-bottom oscillation processwill enable more signals to be acquired for each touch point. The touchsensor 50 comprises a substrate 51 with a front surface 53, a backsurface 55, and connecting end surfaces 57 joining the peripheral region63 of the front surface 53 with the peripheral region 65 of the backsurface 55. The region on the front surface 53 between the portions ofthe peripheral region 63 is the touch region or touch surface 69. Thesubstrate 51 may be made of some form of glass (e.g., soda-lime glass)or other material which overlies a computer display or computing devicedisplay 70, like a liquid crystal display (LCD), a cathode ray tube(CRT), a plasma display, etc. (with an air gap normally therebetween).The composition of the substrate 51 is discussed in more detail below.An object 75 that touches the touch region 69 is shown as a finger, butit is recognized that touches sensed by the surface acoustic waves mayinclude a stylus pressing against the front surface 53 directly orindirectly, through a cover sheet or like element, depending upon theapplication of the touch sensor 50.

In this embodiment of the present invention, the touch sensor 50 takeson the architecture of an “Adler-type” acoustic touch sensor, asdescribed above, that uses two transducers per coordinate axis tospatially spread a transmitted surface acoustic wave signal for thefront surface 53 and two transducers per coordinate axis to spatiallyspread a transmitted surface acoustic wave signal for the back surface55. FIG. 3 b shows a simplified transparent view of the substrate 51that illustrates the arrangement of the operative elements on the twosurfaces 53, 55 of the sensor 50. For clarity, the thickness dimensionof the substrate 51 is greatly exaggerated in the figure. The figureshows, in solid line, the operative elements for the front or topsurface 53 and two transducers for one coordinate axis for the back orbottom surface 55 and, in dotted line, the remainder of the operativeelements for the bottom surface 55. It is understood that the bottomsurface 55 has the same layout for all of the transducers and reflectivearrays as the top surface 53.

Specifically, the touch sensor 50 comprises acoustic transducers 80 a,80 b, 80 c, 80 d that are provided in the peripheral region 63 of thetop surface 53 (see also FIG. 3 b). Note that the touch sensor 50 alsocomprises acoustic transducers 180 a, 180 b, 180 c, 180 d (see also FIG.3 b) that are provided on a border layer 84 of paint or ink in theperipheral region 65 of the bottom surface 55. The purpose of the borderlayer 84 is to suppress around the transducers (and along the associatedarrays shown in FIG. 3 b) oscillation of surface acoustic waves betweentop and bottom surfaces where it is not desired; this is discussed inmore detail below. For the top X-axis coordinate, a first transmittingtransducer 80 a that generates surface acoustic waves is situated on oneside, the top or front surface 53, of the substrate 51 and acorresponding first receiving transducer 80 b that receives therespective generated surface acoustic waves is situated on the oppositeside of the top or front surface 53. The first transmitting transducer80 a generates surface acoustic wave pulses that propagate through thesubstrate 51 across the peripheral region 63 surface along which a firstreflective grating or array 90 a is disposed. The first reflective array90 a is adapted to reflect portions of a surface acoustic waveperpendicularly across the front surface 53 (across the touch surface69) along plural parallel paths to a second reflective array 90 bdisposed on the opposite peripheral region 63 surface. The secondreflective array 90 b is adapted to reflect the surface acoustic wavealong the peripheral region 63 surface to the first receiving transducer80 b where the wave is received for processing. Similarly, for the top Ycoordinate axis, a second transmitting transducer 80 c generates surfaceacoustic wave pulses that propagate through the substrate 51 across theperipheral region 63 surface along which a third reflective grating orarray 90 c is disposed. The third reflective array 90 c is adapted toreflect portions of a surface acoustic wave perpendicularly across thefront surface 53 (i.e., the touch surface 69) along plural parallelpaths to a fourth reflective array 90 d disposed on the oppositeperipheral region 63 surface. The fourth reflective array 90 d isadapted to reflect the surface acoustic wave along the peripheral region63 surface to the second receiving transducer 80 d where the wave isreceived for processing. The propagating surface acoustic waves arerespectively generated and received in each of the two planar coordinateaxes (X and Y) of the front surface 53 of the substrate 51. Thetransducers 80 a, 80 b, 80 c, 80 d are operably coupled to a controlleror control system (not shown), which may be part of a system processorin some embodiments, that is also operably coupled to the display 70.The controller or control system drives the operation of the transducers80 a, 80 b, 80 c, 80 d and measures the signals from such transducers todetermine the touch coordinates, which are then provided to an operatingsystem and software applications to provide the required user interfacewith the display 70.

The bottom surface 55 has the same layout for all of the transducers andreflective arrays as the top surface 53 and which operate in similarfashion. FIG. 3 b shows, in solid line, a first transmitting transducer180 a and a corresponding first receiving transducer 180 b and, indotted line, the first and second reflective arrays 190 a, 190 b for theX coordinate axis for the bottom surface 55. The figure further shows,in dotted line, a second transmitting transducer 180 c and, in solidline, a corresponding second receiving transducer 180 d and the thirdand fourth reflective arrays 190 c, 190 d for the Y coordinate axis forthe bottom surface 55.

The substrate 51 is configured to facilitate surface acoustic wavespropagating on one surface to transfer, through the substrate 51, to theother surface. As noted above, several parameters make this transferpossible, including the transmitting frequency, the distance across thesubstrate (i.e., the top-bottom oscillation distance or beat wavelength)required for a top surface acoustic wave to convert into a bottomsurface acoustic wave (and vice versa), the thickness of the substrate,the acoustic path lengths of the touch sensor, and the composition ofthe substrate. It has been demonstrated that the thinner the substrate,the shorter the distance required for this top-to-bottom energytransfer, if other parameters are generally standard (for example, atransmitting frequency of 5.53.MHz, a substrate composition of eithersoda-lime glass or B270® glass from Schott Glass, and acoustic pathlengths of a typical touch sensor). If the top-bottom oscillationdistance (beat wavelength) is then comparable or short compared to theacoustic path lengths, then the surface wave energy will not bemaintained on a respective signal-launched surface. Consequently, thesurface acoustic wave launched on one surface of the substrate willappear on the other surface. Rapid top-bottom oscillation may beobserved at very small glass thicknesses, for example, 1.1 mm forsoda-lime glass substrate (with a beat wavelength of 47.5 mm at 5.53MHz) and 1.0 mm for B270® glass substrate (with a beat wavelength of36.5 mm at 5.53 MHz). For a substrate composition of soda-lime glass,the surface wave energy will not transfer at substrate thicknessesgreater than 2 mm as previously reported, with experimental indicationsthat 1.8 mm would be sufficient for relatively slow energy transfer. Fora substrate composition of B270® glass, there are experimentalindications that a substrate thickness of 1.35 mm would be sufficientfor a moderate rate of energy transfer.

FIG. 3 c is a schematic view of a touch surface of a substrate of atypical “Adler-type” acoustic touch sensor with sample multiple touchpoints indicated. The figure shows, for the X-axis coordinate, the firsttransmitting transducer (Tx) and the corresponding first receivingtransducer (Rx) and, for the Y-axis coordinate, the second transmittingtransducer (Ty) and the corresponding second receiving transducer (Ry).The figure also shows a first touch point P1 and a second touch point P2on the touch surface. In a one-touch operation, the sensor uses twosurface acoustic wave signals (Tx→Rx from the first transducer pair andTy→Ry from the second transducer pair) to determine the X-axiscoordinate and the Y-axis coordinate of the single touch. In amulti-touch operation, the respective receiving transducer may not havecoordinate information to distinguish between real touch points P1, P2and “ghost touch points”. For example, the first receiving transducer Rxreceives two X-axis perturbations, caused by the two touches P1, P2, inthe surface acoustic wave signal from the first transmitting transducerTx and the second receiving transducer Ry receives two Y-axisperturbations, caused by the two touches P1, P2, in the surface acousticwave signal from the second transmitting transducer Ty. The controlleror control system measures the signals from the transducers but may belimited in determining the matches of the respective X coordinates withthe respective corresponding Y coordinates of the two touches P1, P2.

Specifically, the controller may falsely associate the X coordinate ofthe first touch point P1 with the Y coordinate of the second touch pointP2 leading to a ghost touch position indicated by the lower left dotted“X” in FIG. 3 c and may falsely associate the Y coordinate of the firsttouch point P1 with the X coordinate of the second touch point P2leading to a ghost touch position indicated by the upper right dotted“X” in FIG. 3 c. If the X signal corresponding to acoustic paths fromthe first transmitting transducer Tx to the first receiving transducerRx not only provided precise information on the X coordinate of thefirst touch point P1, but also provided even a rough measure of the Ycoordinate of the first touch point P1, it would be clear which preciseY coordinate from the Y signal between the second transducers Ty, Ry toassociate with the precise X coordinate of the first touch point P1.Similar comments apply to the second touch point P2 as well as to theusefulness of even a rough measure of the X coordinate from Y signals.As will be explained below, the touch sensor 50 of FIGS. 3 a and 3 bprovide such a capability and hence enable resolution of the ambiguityproblem presented in FIG. 3 c. If there are three or more simultaneoustouches, the risks of false associations of X and Y coordinates fromdifferent touches increase in conventional sensor designs and the needfor new methods, as described herein, to resolve such ambiguitiesbecomes more urgent.

FIG. 3 d shows a simplified side view of the touch sensor 50 with acorresponding chart of a touch response in illustrating the specificoperation of the sensor 50. The figure shows, for the top X-axiscoordinate, the first transmitting transducer 80 a that generatessurface acoustic waves situated on one side of the substrate 51 and thecorresponding first receiving transducer 80 b that receives therespective generated surface acoustic waves situated on the oppositeside. The bottom surface 55 has the same layout, i.e., the firsttransmitting transducer 180 a and the corresponding first receivingtransducer 180 b. The respective reflective arrays are not shown forease of visualization. There is a distance L between each of thetransmitting transducers and the respective corresponding receivingtransducer (i.e., the acoustic path length though the touch area), wherethe distance L is substantially smaller in value than the top-bottomoscillation distance (i.e., the beat wavelength λ) of the surfaceacoustic waves generated by a respective transmitting transducer. Theaccompanying chart correlates the distance d from a transmittingtransducer, or more properly its corresponding array (not shown), to atouch with the received signal voltage at each receiving transducer. Thetop first receiving transducer 80 b produces a non-touch response levelL1 and a touch response curve C1 (the signal from the top transducerpair) and the bottom first receiving transducer 180 b produces anon-touch response level L2 and a touch response curve C2 (the signalfrom the bottom transducer pair). Nominally, the non-touch responselevels L1, L2 could be identical, but this is not required asattenuation due to touches may be measured as a percentage or dB changerelative to the non-touch level.

Due to the phenomenon illustrated in FIG. 2, some of the surfaceacoustic wave power transmitted between the top transmitting transducer80 a is transferred to the bottom surface 55 and back up to the topsurface 53 before reaching the top receiving transducer 80 b. Thiseffect of the surface acoustic wave “going underground” particularlyaround the center of the touch region 69 results in reduced attenuationfrom touches on the top surface 53, resulting in the curvature of touchresponse C1. Similarly, the phenomenon illustrated in FIG. 2 leads tosome of the acoustic energy between the bottom transmitting transducer180 a and the bottom receiving transducer 180 b “popping up” andappearing at the top surface 53, resulting in sensitivity to a touch onthe top surface 53 as represented by the shape of the touch response C2.

As the transmitting transducers 80 a, 180 a are generating or launchingsurface acoustic waves across the substrate 51, an object may touch thetouch region 69 of the top surface 53 at a first touch point P3 at afirst distance d and at a later time the object may touch the touchregion 69 of the top surface 53 at a second touch point P4 at a seconddistance d′. The distances d and d′ correspond to the respective Y-axiscoordinate of each touch point.

The first touch point P3 generates a signal loss t (from the topnon-touch response level L1) that the top first receiving transducer 80b detects (and forms part of the touch response curve C1) and a signalloss b (from the bottom non-touch response level L2) that the bottomfirst receiving transducer 180 b detects (and forms part of the touchresponse curve C2). The second touch point P4 generates a signal loss t′(from the top non-touch response level L1) that the top first receivingtransducer 80 b detects (and forms part of the touch response curve C1)and a signal loss b′ (from the bottom non-touch response level L2) thatthe bottom first receiving transducer 180 b detects (and forms part ofthe touch response curve C2). The C1 signal loss t for the first touchpoint P3 which closer to the center is less than the C1 signal loss t′for the second touch point P4 which is closer to an end because more ofthe top propagating surface acoustic wave has “gone underground” to thebottom surface 55 at the center. In contrast, the C2 signal loss b forthe first touch point P3 is more than the C2 signal loss b′ for thesecond touch point P4 because more of the bottom propagating surfaceacoustic wave “pops up” to the top surface 53 at the center. Theseamplitude reductions from the respective non-touch responsesrespectively represent top and bottom touch sensitivity along theacoustic path, as noted above.

The controller or control system measures all of the signals from thereceiving transducers 80 b, 180 b and operates on the signals, such asimplementing an algorithm which compares, for a respective touch point(e.g., touch point P4), the respective ratios of the amplitudes of thenon-touch responses from the bottom transducer pair and the toptransducer pair (e.g., L2/L1) and the amplitudes of the touch responsesfrom the bottom transducer pair and the top transducer pair (e.g., b/tand b′/t′). The latter may be referred to as the ratio of the bottom totop touch sensitivity. With this additional signal information for eachtouch point, in addition to the precise X-axis coordinate informationfrom time delay information, information on the orthogonal Y coordinatemay be determined for a respective touch point on what is conventionallyregarded the X-signal acoustic path. Hence, the controller or controlsystem may then match the precise X-axis coordinate with precise Y-axiscoordinates determined by what is conventionally regarded as theY-signal acoustic path by rejecting any candidate precise Y coordinatethat is not compatible with the Y coordinate determination from theX-signal acoustic path.

An exemplary algorithm, in reduced form, that may be implemented by thesensor 50 for this purpose is b(d)/t(d)={b(L/2)/t(L/2)}·d·(L−d)/(L/2)²,where L is the distance between the transducer pairs on the top andbottom surfaces of the substrate as described above; b(d) is the signalloss for a touch at distance d by the bottom transducer pair asdescribed above; and t(d) is the signal loss for a touch at distance dby top transducer pair as described above. For a touch at the center,d=L/2, the above equation reduces to the correct but trivial relationb(L/2)/t(L/2)=b(L/2)/t(L/2). For touches at the extreme ends, namely d=0or d=L, the above equation reduces to zero as expected from touchresponse curve C2. For L small compared to the beat wavelength λ, theshape of ratio b/t is well approximated by a parabola with a maximum atthe center as is well represented by the above formula. From a measuredvalue of the ratio b(d)/t(d), a value or values of d may be determinedthat satisfy the above equation, hence providing information about theorthogonal coordinate Y from what are nominally the X-signals.Similarly, the sensor 50 is configured and operated to determineorthogonal coordinate X information from what are nominally Y-signals.Thus, a ratio of touch sensitivity along the acoustic path provides anadditional signal (or coordinate information) for the detectioncircuitry of the sensor 50 for determining a respective coordinate ofeach touch point. Note that the sensor 50 obtains generally two valuesof distance d for each value of the ratio of the bottom to top touchsensitivity b/t; the embodiment of FIG. 3 e avoids this complication.

FIG. 3 e is a simplified side view of a second substrate of the sensor50 of FIG. 3 a with a corresponding chart of a touch response. Like theprevious figure, FIG. 3 e shows, for the Y-axis coordinate, the firsttransmitting transducer 80 a that generates surface acoustic wavessituated on one side of the substrate 51 and the corresponding firstreceiving transducer 80 b that receives generated surface acoustic wavessituated on the opposite side. The bottom surface 55 has the samelayout, i.e., the first transmitting transducer 180 a and thecorresponding first receiving transducer 180 b. The respectivereflective arrays are not shown for ease of visualization. There is adistance L between each of the transmitting transducers and therespective corresponding receiving transducer (i.e., the acoustic pathlength across the touch area). The accompanying chart correlates thedistance d of a touch from the transmitting transducers 80 a, 180 a, ormore properly from the corresponding transmitting arrays (not shown),with the received signal voltage at each receiving transducer. However,in this figure, the distance L is one-half of the top-bottom oscillationdistance (i.e., the beat wavelength λ) of the surface acoustic wavesgenerated by a respective transmitting transducer.

Consequently, the configuration of the substrate 51 permits top-bottomoscillation to occur so that surface acoustic wave launched on onesurface of the substrate will appear on the other surface via the energytransfer caused by the action of the Lamb wave modes S₀ and A₀. Thebottom receiving transducer 180 b produces a non-touch response level L1and a touch response curve level D1 (the signal from the top firsttransmitting transducer to the bottom first receiving transducerTt_x→Br_x) and the top receiving transducer 80 b produces a non-touchresponse level L2 and a touch response curve level D2 (the signal fromthe bottom first transmitting transducer to the top first receivingtransducer Bt_x→Tr_x). The sensor 50 operates in similar fashion for therespective Y-axis coordinate elements of the two surfaces 53, 55.Consequently, two ratios of touch sensitivity for a respective touchpoint P may be derived using a similar analysis as previously described:R1≈(Bt_x→Tr_x)/(Tt_x→Br_x) and R2≈(Bt_y→Tr_y)/(Tt_y→Br_y), providing aunique ratio (and additional coordinate information) for each axiscoordinate. As seen in the figure, poor resolution of these ratiosoccurs at the ends of an acoustic path across the touch area while thebest resolution is obtained at or about the midpoint.

Note that, in addition to these touching sensitivity ratios, thedetection circuitry of the sensor 50 also has available for analysis thetouch sensitivity ratio from the touch response curve level D3 (signalTt_x→Tr_x) shown in FIG. 3 f. For the L=Λ/2 case shown in the figure,with no touch, nominally no surface acoustic wave energy from the toptransmitting transducer 80 a reaches the top receiving transducer 80 bbecause when propagating a distance L=Λ/2 the wave is completelytransferred from the top surface 53 to the bottom surface 55. Thus, anon-touch response level L3 of approximately zero is obtained. Theeffect of a touch is to disrupt this perfect transfer of energy betweentop and bottom surfaces resulting in a positive touch response curvelevel D3 for the signal arriving at the top receiving transducer 80 bfrom the top transmitting transducer 80 a. The touch response curvelevel D3 is most sensitive to touch position for values of distance dclose to the end, nicely complementing the lack of end positionsensitivity of the other two touch response curve levels D1, D2. Whilenot shown in FIG. 3 f, the signal Bt_x→Br_x also leads to a touchresponse curve similar to D3 and may also provide for Y coordinateestimation from the nominal X-axis signals. In a similar fashion, thenominal Y-signals Tt_y→Br_y, Bt_y→Tr_y, Tt_y→Tr_y, Bt_y→Br_y provide forX coordinate estimation.

Beneficial effects of oscillation between surface acoustic waves betweenthe top surface 53 and the bottom surface 55 in the touch region 69 havebeen discussed above. In the operation of the sensor 50, it is generallydesired that the oscillation phenomenon is minimized or eliminated whensurface acoustic waves are propagating along the top and bottomreflective arrays 90 a-d, 190 a-d. There are several approaches toaccomplish this. As illustrated in FIG. 3 a, an optional border coating84 may be applied to the back surface 55 but not the front surface 53(or vice versa). With a coating material and thickness chosen tosignificantly alter the Rayleigh wave phase velocity, the symmetrybetween top and bottom surface acoustic waves is broken and there nolonger exist coupled identical oscillators or waves; this effectivelyturns off the oscillation phenomenon. In a related approach, use can bemade of the fact that materials used to fabricate reflective arraysgenerally reduce the Rayleigh wave velocity. By printing the arrays onone surface, for example, the back surface 55 in a negative pattern, thetop and bottom arrays 90 a-d, 190 a-d may be induced to have differentwave velocity-altering effects, thus disrupting the oscillationphenomenon. A third approach is to provide for a substrate 51 with anon-uniform thickness so that the substrate 51 is sufficiently thick inthe regions of the arrays to suppress the oscillation phenomenon. Thisis described in more detail in the above-referenced and incorporatedU.S. patent application by Hecht et al.

FIG. 4 a is a side perspective of a second acoustic touch sensor 200constructed in accordance with the present invention. The touch sensor200 comprises a substrate 205 with a front surface 210, a back surface215, and connecting end surfaces 220 joining the peripheral regions 214of the front surface 210 and of the back surface 215. A connecting endsurface 220 need not be curved as shown but may be any shape thatfacilitates the propagation of surface acoustic waves between the frontsurface 210 and the back surface 215. The substrate 205 is typicallymade of some form of glass or other material that is configured topermit the propagation of surface acoustic waves upon the peripheralregions 214 and the connecting end surfaces 220 and, on thenon-peripheral regions, to facilitate surface acoustic waves propagatingon one surface to transfer, through the substrate 205, to the othersurface. The substrate 205 overlies a computer display or computingdevice display 225, like a liquid crystal display (LCD), a cathode raytube (CRT), plasma, etc. In a bezeled surface acoustic wave touchsensor, the peripheral region of the front surface is covered by a bezelprovided by the housing of the touch sensor or the device integratingthe sensor, since the operative elements, i.e., the transducers andreflective arrays, are on the front surface of the substrate. In azero-bezel or bezel-less surface acoustic wave touch sensor 200, whichis shown in the figure, the peripheral region 214 of the front surface210 is merely the outer/peripheral portion of the front surface 210.Bezel-less surface acoustic wave touch sensors are described in moredetail in commonly-owned U.S. Published Application 2011/0234545,entitled “Bezel-Less Acoustic Touch Apparatus”, which is hereinincorporated by reference. Object 230 is seen as a finger, but it isrecognized that touches sensed by the surface acoustic waves may includea stylus pressing against the front surface 210 directly or indirectly,through a cover sheet or an anti-reflective coating, depending upon theapplication of the touch sensor 200. Acoustic transducers 235 andreflective element arrays (not shown in this figure but described below)are provided on a border layer 227 of opaque paint or ink in theperipheral region 214 of the back surface 215. A mounting or dampingmaterial 250 separates the peripheral region 214 into inside and outsideareas. The transducers 235 are operably coupled to a controller orcontrol system 229 (which may be part of a system processor in someembodiments) that is also operably coupled to the display 225. Thecontroller or control system 229 drives the operation of the transducers235 and measures the signals from such transducers to determine thetouch coordinates, which are then provided to an operating system andsoftware applications to provide the required user interface with thedisplay 225.

FIG. 4 b is a simplified plan view of the back surface 215 of thesubstrate 205. The touch sensor 200 has a mounting or damping material250 that separates the peripheral region 214 around the back surface215, and the operative elements disposed thereon, into two areas: anarea closest to the edge of the substrate 205 (an outside area) and anarea closest to the interior of the substrate 205 (an inside area). Likea conventional acoustic touch sensor, the X-axis and Y-axis pairs oftransducers 235 are disposed at right angles to define a two-dimensionalcoordinate system. In particular, an outside transmitting transducer 235a operates with an outside transmitting reflective array 240 a (X_(T))and an inside receiving reflective array 240 b (x_(R)) and an insidereceiving transducer 235 b. An inside transmitting transducer 235 coperates with an inside transmitting reflective array 240 c (x_(T)) andan outside receiving reflective array 240 d (X_(R)) and outsidereceiving transducer 235 d. Similarly, an outside transmittingtransducer 235 e operates with an outside transmitting reflective array240 e (Y_(T)) and an inside receiving reflective array 240 f (y_(R)) andinside receiving transducer 235 f. An inside transmitting transducer 235g operates with an inside transmitting reflective array 240 g (y_(T))and an outside receiving reflective array 240 h (Y_(R)) and an outsidereceiving transducer 235 h. Consequently, there are two pairs oftransducers 235 and two pairs of reflective arrays 240 for eachcoordinate axis that provide four signals for the sensor 200. Eachtransducer 235 may either transmit or receive a surface acoustic wave,symmetrically. The reflective arrays 240 reflect a surface acoustic wavein a desired direction, as described below.

As noted in FIG. 4 a, the touch sensor 200 is operatively connected witha control system 229 for the associated computer or computing devicethat integrates the sensor 200. The control system 229 generates anelectronic signal that excites the transmitting transducers 235 a, 235c, 235 e, 225 g to generate respective surface acoustic waves (or wavepulses). The control system 229 also receives respective electricalsignals transduced by the receiving transducers 235 b, 235 d, 235 f, 235h from the received surface acoustic waves. The control system 229, asused herein, means electronics typically including a microprocessor withfirmware and analog electronics to generate excitation signals and toreceive back and analyze signals from the touch sensor 200.

FIG. 4 c is a simplified side view of the substrate 205 that illustrates(with additional reference to FIG. 4 b) the operation of the sensor 200.For ease of visualization and description, the figure only shows some ofthe operative elements, specifically, the reflective arrays 240 relatedto the Y-axis coordinates. The outside transmitting transducer 235 egenerates surface acoustic waves that travel along the negative (−)Y-axis direction of the peripheral region 214 of the back surface 215 onwhich the outside transmitting reflective array 240 e (Y_(T)) issituated. The elements of the outside transmitting reflective array 240e (Y_(T)) each transmit part of the surface acoustic waves to anadjacent element of the array 240 e. Also, as seen by the solid linearrow A indicating the wave propagation path, the elements of theoutside transmitting reflective array 240 e (Y_(T)) each couple orreflect part of the surface acoustic waves to travel a) from the outsidetransmitting reflective array 240 e (Y_(T)) outwardly along the negative(−) X-axis direction toward and around the proximate curved connectingsurface 220; and b) along the positive (+) X-axis direction across thefront surface 210 toward the opposing connecting surface 220.

As the surface acoustic waves travel across the front surface 210, theconfiguration and composition of the substrate 205 permits the surfaceacoustic waves to travel to the back surface 215 via the energy transfercaused by the action of the Lamb wave modes S₀ and A₀. The substrate 205then maintains the wave propagation path on the back surface 215 longenough for the waves to travel to the peripheral region 214 of the backsurface 215 and to the inside receiving reflective array 240 f (y_(R)).The elements of the inside receiving reflective array 240 f (y_(R)) eachtransmit the received surface acoustic waves to an adjacent element ofthe array 240 f (y_(R)) so that the waves continue traveling along theinside receiving reflective array 240 f (y_(R)) along the positive (+)Y-axis direction to the inside receiving transducer 235 f.

Similarly, the inside transmitting transducer 235 g generates surfaceacoustic waves that travel along the negative (−) Y-axis direction ofthe peripheral region 214 of the back surface 215 on which the insidetransmitting reflective array 240 g (y_(T)) is situated. The elements ofthe inside transmitting reflective array 240 g (y_(T)) each transmitpart of the surface acoustic waves to an adjacent element of the array240 g (y_(T)). Also, as seen by the solid line arrow B indicating thewave propagation path, the elements of the inside transmittingreflective array 240 g (y_(T)) each couple or reflect part of thesurface acoustic waves to travel a) from the inside transmittingreflective array 240 g (y_(T)) inwardly along the positive (+) X-axisdirection away from proximate curved connecting surface 220. As thesurface acoustic waves travel across the back surface 215, theconfiguration and composition of the substrate 205 permits the surfaceacoustic waves to travel to the front surface 210 via the energytransfer caused by the action of the Lamb wave modes S₀ and A₀. Thewaves continue along the positive (+) X-axis direction such that thesubstrate 205 maintains the wave propagation path on the front surface210 long enough for the waves to travel to the peripheral region 214 ofthe front surface 210 and then a) around the proximate curved connectingsurface 220; and b) along the negative (−) X-axis direction to theoutside receiving reflective array 240 h (Y_(R)). The elements of theoutside receiving reflective array 240 h (Y_(R)) each transmit thereceived surface acoustic waves to an adjacent element of the array 240h so that the waves continue traveling along the outside receivingreflective array 240 h (Y_(R)) along the positive (+) Y-axis directionto the outside receiving transducer 235 h.

It is understood that the sensor 50 is configured and operated insimilar fashion for the operative elements related to the X-axiscoordinates. Specifically, the outside-inside transmitting transducers235 a, 235 c; the outside-inside receiving transducers 235 d, 235 b; theoutside-inside transmitting reflective arrays 240 a (X_(T)), 240 c(x_(T)); and the outside-inside receiving reflective arrays 240 d(X_(R)), 240 b (x_(R)) operate in the same fashion for the X-axiscoordinate direction.

A touch of the touch region on the front surface 210 by an object 230,such as finger or stylus, absorbs a portion of the energy of the surfaceacoustic waves propagating across the front surface 210 and causes anattenuation of the waves passing through the point of touch. Theresulting attenuation is detected by the receiving transducers as aperturbation in the acoustic signal. The control system 229 processesand analyzes all of the electrical signals transduced by the receivingtransducers, including those related to waveform perturbations, todetect the touch coordinates and position information in a mannersimilar to that described above, for example, with respect to FIG. 3 e.Further, the control system 229 maps the touch coordinates and positioninformation to the appropriate control actions of the user interfaceshown in the display 225 that is generally placed behind the backsurface 215.

For example, the control system 229 uses the touch dip delay times inthe Y-axis coordinate signals to provide the Y-axis coordinatemeasurement. The control system derives the X-axis coordinatemeasurement, using the previously-described analysis, from the ratio ofthe dip strengths, i.e., the touch sensitivities, in the top-bottomoscillation signals Y_(T)→y_(R) and y_(T)→Y_(R). Thus, the acoustictouch sensor 200 provides an XY coordinate multi-touch input devicesystem.

Advantageously, the sensor 200 enables the entire top surface 210 to beacoustically active. With no bezel required and maximal touch sensitivesurface area, this is in keeping with market trends for increasinglysleek and space efficient product designs.

It is noted that a design rule for rounded substrate edges in certainbezel-less touch sensors require the edge radius to be greater than orequal to 1.5 mm at the standard transmitting frequency 5.53 MHz. Thismitigates so-called Lamb parasitic signal paths, accompanying the use ofrounded substrate edging, that parallel the surface acoustic wavepropagation path on the touch region and present parasitic signals atthe receiving transducers. However, with a small thickness substratethat permits top-bottom oscillation, e.g., 1.6.mm (which is fixed by adesired beat wavelength), the edge radius may be much less than thedesign rule dimension (e.g., less than or equal to 0.8 mm for a 1.6. mmsubstrate at 5.53 MHz). This results because the sensor 200 isconfigured so that some of the conversions of propagating surfaceacoustic waves to Lamb parasitic signals, and vice versa, may beblocked. For example, the surface acoustic waves generated by theoutside bottom transmitting transducer 235 e will travel around theproximate connecting surface 220 along the top surface 210, convert intoa surface acoustic wave propagating along the back surface 215, and bereceived by the bottom inside receiving transducer 235 f. At the sametime, the Lamb parasitic signals generated by the surface acoustic wavespropagating around the proximate connecting surface 220 will travelalong the top surface 210 and around the connecting surface 220 at thereceiving end of the substrate 205 and then blocked on the way towardsthe bottom inside receiving array 240 f and transducer 235 f by themounting or damping material 250. The sensor 200 similarly suppresses,for other signals of the sensor 200, parasitic signals associated withthe use of curved edged substrates.

As noted with respect to FIG. 3 e, poor resolution of the touchingsensitivity ratios occurs at the ends of the acoustic path through thetouch area while the best resolution is obtained at or about themidpoint. This is illustrated in FIG. 5 which shows a graph of the touchsensitivity of the top-bottom oscillation signals Y_(T)→y_(R) (denotedas curve A to relate to the propagation path A in FIG. 4 c) andy_(T)→Y_(R) (denoted as curve B to relate to the propagation path B inFIG. 4 c) versus the distance across the X-axis of the substrate 205.The ratio of the touch dip strengths of the two signals Y_(T)→y_(R) andy_(T)→Y_(R) slowly vary near the borders of the substrate 205. Thecontrol system 229 may correct this resolution by processing thosesignals with the strong variation of touch sensitivity peak provided bya bottom-top-and-back-to-bottom oscillation signal y_(T)→y_(R) from theinside transmitting transducer 235 g to the inside receiving transducer235 f (denoted as curve G which is similar to touch response curve levelD3 of FIG. 3 f).

FIGS. 6 a-6 d illustrate the use of a sensor of the present invention toresolving touch overlap problems in dual-touch or multi-touch. FIG. 6 ashows a simplified plan view of an Adler-type sensor 300 having asubstrate 301 with a top surface 302 and a bottom surface 303. Further,for an X-axis coordinate determination, the top surface 302 has a toptransmitting transducer T_(Tx) and the bottom surface 303 has a bottomtransmitting transducer B_(Tx), both represented by the transmittingtransducer Tx 305; transmitting reflector arrays 307 on the top surface302 and on the bottom surface 303; receiving reflector arrays 309 on thetop and bottom surfaces 302, 303; and receiving transducers T_(Rx) andB_(Rx) both represented by the receiving transducer Rx 311 (note thatthe bottom surface elements are not shown in the figure). As in FIG. 3b, top surface 302 and bottom surface 303 have similar arrangements ofoperative elements. The figure also shows by dotted line arrows anacoustic path of a top launched surface acoustic wave and two touches A,B of the touch region of the top surface 302 that overlap to some degreealong the same acoustic path. The figure also shows two touches C, Dthat occur on different acoustic paths.

The sensor 300 has no problem detecting the respective X-axis coordinatefor each of the two touches C, D that occur on different acoustic pathsbecause each touch generates different time delays of the perturbed wavethat can be detected and analyzed by the sensor 300. In the case of thetwo touches A, B that overlap along the same acoustic path, the sensor300 cannot resolve easily by conventional means the precise X-axiscoordinates as the attenuation shadows of the two touches are confoundedtogether resulting in only one determined X-axis coordinate that onlyroughly approximates the two different X-axis coordinates of the twotouches A and B.

FIG. 6 b shows, for the X-axis coordinate, a graph of the receivedsignal versus the delay time of the received signal for the sensor 300.Three curves denote three signals (the signal B_(Tx)→B_(Rx) from thebottom transmitting transducer to the bottom receiving transducer; thesignal T_(Tx)→B_(Rx), from the top transmitting transducer 305 to thebottom receiving transducer via top-bottom oscillation; and the signalB_(Tx)→T_(Rx) from the bottom transmitting transducer to the topreceiving transducer 311 via top-bottom oscillation) processed by thesensor 300 and the approximate touch dip strengths of the signals causedby the two touches A, B. The sensor 300 analyzes and operates on thissignal information to isolate each touch A, B and their respective touchdip strength. FIG. 6 c shows the resulting isolation of one touch A,mathematically described as (signal T_(Tx)→B_(Rx))−α(signalB_(Tx)→T_(Rx)) and FIG. 6 d shows the resulting isolation of the othertouch B, mathematically described as (signal B_(Tx)→T_(Rx))−βsignalT_(Tx)→B_(Rx)), where the constants α and β are adjusted to minimize therespective dip width. In this way, the sensor 300 may be able todistinguish the different delay times of the perturbed waves caused bythe two touches A, B for the respective axis direction.

Other modifications are possible within the scope of the invention. Forexample, in each embodiment described, the substrate may take on varioussizes and shapes depending upon engineering or applicationconsiderations. Moreover, the substrate may be adapted to optimizeeither the energy transfer, the maintenance of propagation on arespective surface, or both. The substrate may also take on differentcompositions other than glass, such as aluminum or stainless steel, thatcan facilitate both the maintenance of propagating surface acousticwaves and the transfer of propagating surface acoustic waves from onesurface, through the substrate, to the other surface, as desired.

Also, the sensors may utilize various means to affect the energytransfer or the maintenance of propagation on a respective surface.Also, as noted above, depending upon various factors, the substrate mayutilize different thicknesses to maintain surface acoustic wavespropagating on a respective surface and as well as utilize differentthicknesses to convert a top surface acoustic wave into a bottom surfaceacoustic wave (and vice versa).

Further, the present invention may be extended to acoustic touch sensorsutilizing three axis directions, e.g., XYU axes, providing surfaceacoustic wave signals for the U-axis direction as well as the X-axis andY-axis directions. In this case, the U₁ (X_(Tx)→Y_(Rx)) axis wouldobtain four signals and the U₂ (Y_(Tx)→X_(Rx)) axis would obtain foursignals. Thus, the U-axis would have a total of eight different signalsand the XYU axes as a whole would have a total of sixteen differentsignals.

What is claimed:
 1. An acoustic touch apparatus that distinguishessimultaneous touches, comprising a substrate that is adapted to utilizea transfer of surface acoustic waves, through the substrate, betweenopposite surfaces of the substrate to vary touch sensitivity along arespective acoustic path across a substrate touch region and acoustictransducers that are adapted to transmit and receive surface acousticwaves travelling on the opposite substrate surfaces, said substratetouch region providing additional signal information of touch responsesof receiving transducers sufficient to permit the apparatus to determinean axis coordinate of a respective touch on the substrate touch region.2. The apparatus of claim 1, wherein the additional signal informationcomprises a comparison of the touch responses of receiving transducerswith non-touch responses of the receiving transducers.
 3. The apparatusof claim 1, wherein the additional signal information comprises acomparison of the signal level changes of the touch responses ofreceiving transducers.
 4. An acoustic touch apparatus, comprising: asubstrate that has top and bottom surfaces; a transmitting and receivingacoustic wave transducer pair on the top surface that is adapted totransmit and receive surface acoustic waves therebetween across a touchregion on the top surface and to produce a touch response signal for atouch on the touch region; a transmitting and receiving acoustic wavetransducer pair on the bottom surface that is adapted to transmit andreceive surface acoustic waves therebetween, said substrate beingadapted to propagate surface acoustic waves along each surface and totransfer, through the substrate, surface acoustic waves between thesurfaces sufficient to enable a touch on the top surface to produce atouch response signal by the bottom surface transducer pair; and acontroller that operates on the touch response signals and non-touchresponse signals produced by each of the bottom surface transducer pairand the top surface transducer pair and determines positionalinformation of a touch on the touch region from the response signals. 5.The apparatus of claim 4, wherein the controller operates on theresponse signals to determine the top and bottom touch sensitivity alongan acoustic path across the touch region.
 6. The apparatus of claim 5,wherein the top and bottom sensitivity is represented by the reductionin amplitude of the touch response signal to the non-touch responsesignal for each of the bottom surface transducer pair and the topsurface transducer pair.
 7. The apparatus of claim 6, wherein thecontroller determines positional information of a touch by comparing theamplitude reductions of the touch response of the bottom surfacetransducer pair to the touch response of the top surface transducerpair.
 8. The apparatus of claim 6, wherein the controller determinespositional information of a touch by applying the following relation:b(d)/t(d)={b(L/2)/t(L/2)}·d·(L−d)/(L/2)², where L is the distancebetween the transducers in a respective transducer pair on the top andbottom surfaces; b(d) is the amplitude reduction of the touch responsefor a touch at distance d by the bottom surface transducer pair; andt(d) is the amplitude reduction of the touch response for a touch atdistance d by the top surface transducer pair.
 9. The apparatus of claim5, wherein the substrate is adapted to propagate surface acoustic wavesalong each surface and to transfer, through the substrate, surfaceacoustic waves between the surfaces sufficient to enable a touch on thetop surface to produce a respective touch response signal between thetop surface transmitting transducer to the bottom surface receivingtransducer, and the bottom surface transmitting transducer to the topsurface receiving transducer.
 10. The apparatus of claim 9, wherein thetop and bottom sensitivity is represented by the reduction in amplitudeof the touch response signal to the non-touch response signal betweenthe bottom surface transmitting transducer to the top surface receivingtransducer, and the top surface transmitting transducer to the bottomsurface receiving transducer.
 11. The apparatus of claim 10, wherein thecontroller determines positional information of a touch by comparing theamplitude reductions of the touch response of the bottom surfacetransmitting transducer to the top surface receiving transducer, to thetouch response of the top surface transmitting transducer to the bottomsurface receiving transducer.
 12. The apparatus of claim 11, wherein thecontroller determines positional information of a touch by furtheranalyzing the amplitude changes of the touch response of the bottomsurface transducer pair and of the touch response of the top surfacetransducer pair.
 13. The system of claim 9, wherein the controllerdetermines positional information of overlapping touches on the topsurface by utilizing a comparison of the touch response signal betweenthe top surface transmitting transducer to the bottom surface receivingtransducer with the touch response signal between the bottom surfacetransmitting transducer to the top surface receiving transducer for eachtouch to distinguish between the signals of the touches and therespective positional information.
 14. An acoustic touch sensor systemhaving multi-touch capability, comprising: a substrate that is capablein a peripheral region to propagating surface acoustic waves alongsubstrate surfaces and in a central region to permit top-bottomoscillation of the surface acoustic waves from the one of the surfacesto the other surface through the substrate, said substrate having a topsurface, a bottom surface, and a curved connecting surface formedbetween said top surface and said bottom surface; a first transmittingelement disposed on an outside area of the peripheral region of thebottom surface and a second transmitting element disposed on an insidearea of the peripheral region of the bottom surface; a first receivingelement disposed on an outside area of the peripheral region of thebottom surface and a second receiving element disposed on an inside areaof the peripheral region of the bottom surface, the set of transmittingelements and the set of receiving elements disposed on opposing sides ofthe central region of the substrate; and a controller that excites thefirst and second transmitting elements to generate respective surfaceacoustic waves and that analyzes the respective signals received by thefirst and second receiving elements, said substrate forming at leastrespective wave paths from the first transmitting element, around theproximate curved connecting surface, through the substrate in thecentral region and to the second receiving element; and from the secondtransmitting element, through the substrate in the central region,around the proximate curved connecting surface and to the firstreceiving element.
 15. The system of claim 14, wherein each transmittingelement comprises a transmitting acoustic wave transducer and anassociated transmitting reflective array and each receiving elementcomprises a receiving acoustic wave transducer and an associatedreceiving reflective array.
 16. The system of claim 14 furthercomprising another set of transmitting elements and another set ofreceiving elements disposed on the other two opposing sides of thecentral region of the substrate in a similar manner as the respectivefirst sets, each pair of sets being utilized to define a respective axiscoordinate of the front surface.
 17. The system of claim 14, whereineach receiving element is adapted to produce a touch response signal fora respective touch on the top surface and the controller analyzes thetouch response signals and non-touch response signals produced by eachreceiving element to determine axis coordinate information of the touchon the top surface from the response signals.
 18. The system of claim17, wherein the controller analyzes the ratios of signal losses of touchresponse signals to determine axis coordinate information of the touchon the top surface.
 19. The system of claim 17, wherein the controlleranalyzes the delay times of touch response signals, and the ratios ofsignal losses of touch response signals in the top-bottomoscillation-based signals to determine axis coordinate information ofthe touch on the top surface.
 20. The system of claim 19, whereincertain of the axis coordinate information is dependent upon the ratiosof signal losses of touch response signals in the top-bottomoscillation-based signals; and the distance between respectivetransmitting and receiving elements on the top and bottom surfaces. 21.The system of claim 19, further comprising another set of transmittingelements and another set of receiving elements disposed on the other twoopposing sides of the central region of the substrate in a similarmanner as the respective first sets, each pair of sets being utilized todefine a respective axis coordinate of the front surface.
 22. The systemof claim 17, wherein the controller analyzes the ratios of signal levelchanges of touch response signals to determine axis coordinateinformation of the touch on the top surface.
 23. The system of claim 14,wherein the substrate further has a damping material separating theperipheral region into outside and inside areas.
 24. The system of claim14, wherein the substrate is adapted to provide non-symmetrical top andbottom surfaces acoustic waves in a peripheral region in order topropagate surface acoustic waves.